A novel mantle-margin gland system in <i>Tectura virginea</i> (Patellogastropoda)

Glandular defensive systems remain poorly understood in many marine invertebrates. Here, we investigated the anatomy and chemical composition of mantle-margin glands in the true limpet Tectura virginea. These glands produce a persistent, thread-like secretion that emerges from the exposed mantle edge in response to mechanical stimulation. Light and electron microscopy revealed large glands, each dominated by a single voluminous secretory cell surrounded by quiescent precursors and ring musculature, suggesting a holocrine expulsion mechanism. Liquid chromatography-mass spectrometry identified over 80 compounds, including disulfides, sulfonates and organic acids. Their presence suggests that the secretion may act as a chemical barrier against microbial colonization or small invertebrate predators. Several major compounds, such as 1-(propyldisulfanyl)-1-(propylsulfinyl)propane, have potential defensive roles. The anatomical position of the glands and the biochemical diversity of their products suggest a defensive role. Our findings support the interpretation of these mantle-margin glands as a novel repugnatorial system, representing a unique adaptation among patellogastropods. These findings highlight the potential for secretory and defensive functions in the mantle-margin glands of T. virginea, underscoring the broader relevance of such glands in less-studied lineages.